1. Field of Invention
The present invention relates to a semiconductor device in which a display device and a control circuit are provided over an insulating substrate. In particular, the present invention relates to a display device including a thin film transistor (hereinafter referred to as a TFT) over an insulating substrate such as a glass substrate, or a plastic substrate and a semiconductor device including a control circuit.
2. Related Art
In late years, expectations for a so-called “system on panel” in which a driver circuit and a control circuit as well as a display device such as a liquid crystal display device are integrally formed over an insulating substrate such as a glass substrate or a plastic substrate are increased. The control circuit here refers to a CPU, a memory, a controller, and the like.
Using such a “system on panel”, weight saving, cost reduction, miniaturization, lower power consumption, and improvements in reliability of a semiconductor device are expected.
When an external input unit is used for such a system on panel, a connector of the input unit can obstruct miniaturization and can also be a major factor of the bottleneck of the reliability. Accordingly, by arranging the input unit including a keyboard in the same substrate, such a system on panel can be more sophisticated.
As for an existing semiconductor device, input operation is performed by pushing or touching a button-like input unit with a finger or the like.
For example, a liquid crystal display device often uses glass for a counter substrate. When an input unit is to be integrated on the glass substrate, it is desirable to form buttons from glass directly on the substrate; however, that is not easy due to the nature of the material.
Further, when plastic is employed for the counter substrate, the number of steps is increased by forming the button into the liquid crystal display device; therefore, reduction in yield or reduced reliability can be caused.